Krill Oil vs. Fish Oil for Dogs and Cats: Benefits, Differences, and How to Choose

pet supplements Sep 25, 2026

By Dr. Katie Woodley, BVSc, cVMA, GDVCHM, CVNN

Many dogs and cats receive an omega-3 supplement for skin, coat, or joint support. Yet some continue to have symptoms, and testing may show lower EPA and DHA levels than expected. This can leave pet parents wondering whether the supplement is helping.

Dr. Katie Woodley, integrative veterinarian and founder of The Natural Pet Doctor, recommends starting with the product label and the pet’s complete diet. The amount of oil listed on a bottle is not the same as the amount of EPA and DHA it provides. Product quality, storage, individual tolerance, and the underlying cause of a pet’s symptoms also affect the decision.

The short answer: Krill oil and fish oil can both provide EPA and DHA, the marine omega-3 fats dogs and cats can use directly. Krill carries much of these fats in phospholipids and contains choline-related compounds and astaxanthin. Fish oil can be just as reasonable a choice when it is fresh and supplies enough EPA and DHA. The right option depends on the pet, the label, and the quality of the oil.

The most useful starting point is the amount of EPA and DHA listed per serving, followed by a review of the product’s quality and suitability for the individual pet.

Companion video: Krill Oil vs. Fish Oil: Which Omega-3 Is Better for Dogs & Cats?

Key Takeaways

“Omega-3” on a label may mean plant-based ALA rather than preformed EPA and DHA.
A 1,000 mg fish-oil capsule does not necessarily contain 1,000 mg of EPA and DHA.
Small dog studies show differences in blood fatty-acid levels between krill and fish sources. They do not prove that krill is best for every pet.
Freshness, testing, storage, and the pet’s tolerance matter as much as the name of the oil.
Persistent itching, stiffness, or gut symptoms still call for a veterinary evaluation.

Jump to a Section

What EPA and DHA do for pets
Fish, krill, flaxseed, roe, and algae compared
What the krill research shows
Why levels may stay low
How to read the label
Freshness and storage
How much a pet may need
Product examples
Safety and frequently asked questions

Check the EPA and DHA Before Buying Another Bottle

Record the milligrams of EPA and DHA in the current supplement’s daily serving. If the label lists only “total omega-3” or “fish oil,” ask the manufacturer for the individual amounts. The label example below shows why the distinction matters.

What do EPA and DHA do for dogs and cats?

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are marine omega-3 fats that become part of cell membranes. DHA has an especially important role in the brain and eyes. EPA and DHA also help regulate inflammatory signals, which is why they come up in conversations about itchy skin, joint comfort, and healthy aging.

Inflammation also has an active resolution phase. EPA and DHA are precursors to specialized pro-resolving mediators, molecules that help bring an inflammatory response to an appropriate close and support tissue recovery. This mechanism does not mean an omega-3 supplement will resolve the cause of a pet’s chronic symptoms. It is one potential component of a broader nutrition and veterinary care plan.

Dry skin, paw chewing, and reduced mobility are not specific signs of an omega-3 deficiency. Allergies, infection, pain, and other conditions can produce similar changes and should be evaluated separately.

Omega-3 Sources at a Glance

An “omega-3” claim does not identify which fatty acids a product contains. When the goal is to provide EPA and DHA, the label should state the amount of each per serving.

Source	Main omega-3s	What to know
Flaxseed, chia, or hemp	ALA (alpha-linoleic acid)	ALA has its own nutritional role, but conversion to EPA and DHA is limited, particularly in cats. These ingredients should not be assumed to replace a direct EPA/DHA source.
Fish oil	Preformed EPA and DHA	A practical, often cost-effective option when concentration, purity, and freshness are clear. Fish oils can differ in fatty-acid form and formulation.
Krill oil	Preformed EPA and DHA, much of it in phospholipids	Also contains phosphatidylcholine and astaxanthin. Compare the actual EPA/DHA dose and cost per serving.
Fish roe oil	Preformed EPA and DHA, including phospholipid-associated fats	Composition varies by species and product; read the label rather than assuming it matches krill.
Marine algae oil	DHA and, in some products, EPA	A direct marine-derived alternative; check whether the specific product supplies both fats and is suitable for pets.

Flaxseed and chia supply ALA, a plant omega-3. Dogs convert only some of it into EPA and DHA; cats do so very poorly. That is why flaxseed on a food label is not a stand-in for a stated amount of marine EPA and DHA. It can still be a useful food ingredient for other reasons.

In a study of 45 dogs, diets containing fish or krill increased the omega-3 index over four weeks, whereas the flaxseed diet did not produce a significant increase. Because the diets supplied different amounts of EPA and DHA, the study does not establish that one marine oil is superior to another. Coconut oil provides neither EPA nor DHA and should not be counted as a marine omega-3 source.

What the Krill Oil Research Actually Shows

The evidence supports a more specific comparison than a blanket recommendation for either oil. In a six-week study of 20 Alaskan Huskies, one group received krill meal and the other received fish oil with comparable EPA and DHA intake. Red blood cell EPA and the overall omega-3 index increased more in the krill group, while DHA increased more in the fish-oil group.

The study measured fatty-acid incorporation into red blood cells. It did not measure improvement in skin disease, joint pain, or other clinical outcomes. Krill’s phospholipid structure may contribute to differences in incorporation, but both oils supplied absorbable EPA and DHA. These findings do not establish a universal dose or a clinical advantage for every krill product.

Krill also contains phosphatidylcholine, a source of choline, and naturally occurring astaxanthin, the pigment responsible for its reddish color. In a canine study, krill-derived phosphatidylcholine increased plasma choline and related metabolites. The study did not establish that krill oil treats cognitive or liver disease. Astaxanthin does not remove the need for appropriate processing and storage.

Direct comparative research in cats is limited. For an individual cat, palatability, tolerance, and the amount of EPA and DHA provided are practical considerations; canine results alone cannot establish which source is preferable for cats.

Why a Pet May Still Have Low Omega-3 Levels

Several factors should be reviewed before changing products:

The label emphasizes total oil, not EPA and DHA. A “1,000 mg fish oil” capsule contains 1,000 mg of oil, not necessarily 1,000 mg of EPA plus DHA.
The product mainly contains ALA. A pet food can truthfully advertise omega-3s from flaxseed while supplying little preformed EPA and DHA.
The amount given is small relative to the pet’s diet or clinical goal. Serving sizes and concentrations vary widely.
The oil is old, poorly stored, or inconsistently given. Omega-3 fats are vulnerable to heat, oxygen, and light.
Another health issue affects the pet’s response. Ongoing gastrointestinal disease, poor appetite, or a separate cause of itching or stiffness warrants veterinary assessment rather than repeatedly increasing oil.

The existing diet is part of this assessment. Some foods supply declared amounts of EPA and DHA, while others list only total omega-3s. The amount from food and supplements should be considered together.

How to Read an Omega-3 Supplement Label

Dr. Woodley recommends three checks when comparing products:

Find the EPA and DHA numbers. For example, a capsule listing 180 mg EPA and 120 mg DHA supplies 300 mg combined EPA/DHA, even if the front says “1,000 mg fish oil.”
Look at the source. Is it fish, krill, fish roe, algae, or primarily flaxseed? The answer helps explain what the “omega-3” claim actually means.
Ask how the oil is tested and protected. Look for contaminant and oxidation testing, a usable expiration date, packaging that limits light and air, and clear instructions for storage after opening.

Action step: Photograph the product’s front label and supplement-facts panel. Share them with the veterinarian alongside the pet’s current food label so the total EPA and DHA intake can be assessed.

Smaller fish such as sardines and anchovies are common sources, but species alone does not prove purity. A reputable manufacturer’s contaminant results are more useful than broad claims that any ocean or species is completely free of pollutants. One analysis of 11 canine fish-oil supplements found several instances in which measured EPA and/or DHA did not meet label claims within the study’s five-percent comparison margin. The finding supports product-specific quality checks rather than conclusions about every fish oil.

Manufacturers may provide peroxide, anisidine, or total oxidation (TOTOX) results as measures of oxidative quality. Interpretation depends on the product and testing method. Protective packaging is valuable, but a dark bottle or certification seal alone cannot verify the EPA/DHA content or the condition of an opened oil.

How to Tell if an Omega-3 Oil Has Gone Bad

A mild marine odor may be normal. A sharp, sour, paint-like, or rotten smell is a reason to stop using the oil and contact the manufacturer. A pet’s sudden refusal of a previously accepted oil may also prompt you to check the product’s expiration date and storage history.

Odor is an imperfect measure of quality. Follow the manufacturer’s storage instructions, close the container promptly, and protect it from heat and sunlight. Choose a bottle size that can be used within the recommended period after opening.

How Much Omega-3 Does a Dog or Cat Need?

The appropriate amount depends on the pet’s weight, diet, medical conditions, and reason for supplementation. Calculate the EPA and DHA in the daily serving and account for any amounts provided by the food. A veterinarian can then assess whether the total fits that individual pet.

Marine oils add fat and calories and may cause gastrointestinal upset, especially when introduced too quickly. Blood fatty-acid levels can change within weeks, while changes in skin or mobility may take longer and depend on the underlying condition. Persistent symptoms alone are not a reason to increase the dose.

For dogs, an omega-3 index test can sometimes help assess EPA/DHA status and changes after a consistent dietary plan. It measures red-blood-cell fatty acids; it cannot diagnose why a pet is itchy or stiff. Check test availability and interpretation for the species. Human or dog ranges should not be applied to cats without validation.

Action step: If you've given a supplement consistently and its effect is unclear, review the label, diet, symptoms, and any test results with your veterinarian before changing the dose.

Omega-3 Products Dr. Woodley Considers

The following products represent different omega-3 sources Dr. Woodley considers. Their current EPA/DHA content, testing information, and serving instructions should be checked for the individual pet.

Feline Essential Antarctic Krill Oil for Cats and Dogs — an Antarctic krill option for households seeking a phospholipid-rich marine oil. Check the EPA/DHA per serving for the individual pet. Cats tend to accept this brand well.
Nordic Naturals Omega-3 Pet — a traditional fish-oil option. Pet-specific sizes can make it practical when a larger dog needs more daily EPA/DHA.
Proactive Paws Roe Mega — a fish-roe and small-fish-oil combination for pet parents interested in another phospholipid-containing source. Review the current label and economics for the pet’s size.

Palatability may determine whether a cat will accept a product consistently. For larger dogs, EPA/DHA concentration also affects the volume and cost of a daily serving. Product selection should account for both.

When to Check With a Veterinarian First

Veterinary review is especially important for pets with a history of pancreatitis or fat intolerance, a fish or crustacean reaction, a bleeding disorder, an upcoming procedure, or a therapeutic diet with controlled fat content. The veterinarian should also review medications and other supplements, particularly those that may affect clotting.

Excess oil can cause gastrointestinal upset and add substantial calories. Unusual bruising or bleeding requires veterinary attention, as do persistent itching, vomiting, diarrhea, and changes in mobility, regardless of supplement use.

Frequently Asked Questions

Can cats take krill oil?

Cats can receive an appropriately formulated krill oil when its ingredients and dose suit the individual cat. Because cats convert plant ALA to long-chain omega-3s poorly, preformed EPA and DHA are the relevant label numbers. There is insufficient direct feline evidence to say krill is always better than fish oil.

Is flaxseed enough omega-3 for dogs or cats?

Flaxseed supplies ALA, which is a plant-based omega. It does not supply meaningful preformed EPA and DHA. It may have a place in a balanced diet, but it should not automatically be treated as equivalent to a marine EPA/DHA source, especially for cats.

Is algae oil an alternative to fish oil for pets?

Some marine algae oils provide preformed DHA and some also supply EPA. The exact fatty-acid profile, pet suitability, and concentration should be checked on the label. “Algae oil” alone does not guarantee both EPA and DHA.

Is fish roe oil the same as krill oil?

No. Fish roe comes from fish eggs; krill oil comes from small crustaceans. Both may contain phospholipid-associated omega-3s, but the EPA/DHA amounts and other ingredients depend on the product.

How long does an omega-3 supplement take to work?

Fatty-acid levels may shift within weeks, but a change in coat, comfort, or other signs is not guaranteed on a fixed schedule. A pet with persistent symptoms needs a diagnosis and follow-up plan, even if omega-3 intake improves. It can take up to 3-4 weeks of consistent omega-3 use before you may see results.

The Next Step

Before selecting an omega-3 supplement, confirm the source, the EPA and DHA amount per serving, the manufacturer’s quality testing, and storage instructions. Fish, krill, fish roe, and some algae oils provide preformed EPA and DHA; flaxseed and chia primarily provide ALA.

If a pet continues to have symptoms despite supplementation, review the complete diet and the product with a veterinarian. Appropriate omega-3 intake may support health, but persistent itching, digestive problems, or reduced mobility still require an assessment of the underlying cause.

For a closer look at krill’s phospholipids and the comparison with fish oil, watch Dr. Woodley’s companion video above. Pet parents who want to measure their dog’s fatty-acid status can also explore the omega-3 index test and discuss whether testing makes sense for their dog.

About the Author

Dr. Katie Woodley, BVSc, cVMA, GDVCHM, CVNN, is an integrative veterinarian and founder of The Natural Pet Doctor. She teaches pet parents how to look beyond recurring symptoms and build a nutrition and health plan with their local veterinarian. Her work focuses on gut and skin health, functional testing when useful, food therapy, and whole-pet care.

References

Disclaimer: This article is for general education and does not diagnose or treat an individual animal. A veterinarian should review new, persistent, or worsening symptoms, medical conditions, medications, and the appropriate supplement and dose for the pet. Statements about supplements in this article have not been evaluated by the Food and Drug Administration. The products mentioned are not intended to diagnose, treat, cure, or prevent disease. Some links below are affiliate links. The Natural Pet Doctor may earn a commission at no additional cost to the purchaser.